Sniper rifle zooming:
Hold R3 to zoom in to the maximum with the sniper rifle. Alternately, hold R + R3.

Mogadishu Mile mission:
As soon as the mission starts, run in front of the last AAV. Jump on the front of it and catch a free ride to the end of the mission. By doing this, you will be on top of it when they speed up and will not have to catch up. This results in you completing the mission faster and easier.